1. Field of the Invention
The present invention relates to a technique of estimating a load applied to an output axis of a motor of an elevator car, and compensating a torque command current of the motor, and in particular to a leveling control device for an elevator system used for a level correction operating by a level difference between a designated floor bottom and an elevator car bottom generated when passengers get in/off after the elevator car stops at the designated floor.
2. Description of the Background Art
In general, a torque compensation method of compensating a torque corresponding to a load detected during movement by employing a load detector detecting a load of an elevator car (hereinafter, referred to as `car`) has been used in order to improve a ride comfort in an elevator system. According to the torque compensation method, there is a sufficient time to detect the load before closing a car door and moving the car, and thus the load of the car can be exactly detected. As a result, it is possible to control the motor to generate a torque compensation command appropriate to an amount of the detected load, and thus the ride comfort is relatively good.
However, when the car stops at the designated floor, the door is open and the passengers get in or off the car, a bottom level of the car is not identical to a bottom level of the designated floor according to a load variation, that is a level difference is generated. Here, the level difference is detected by using a position detection unit disposed at an upper portion of the car, and then out a level correction operating is carried out. However, the passengers constantly get in or off while the level correction operating is performed, and thus the load amount detected by the load detector has an error. Therefore, a speed control property of the elevator system compensating the load of the car is worsened. The conventional leveling control device for the elevator system will now be described in detail with reference to FIG. 1.
In order to move the car in an elevator system employing an alternating current motor, in case a torque of the alternating current motor is controlled by dividing a control current supplied to the alternating current motor into two vectors, namely a torque component current and a magnetic flux component current, an almost identical property to the control property of a direct current motor can be obtained. Accordingly, the vector control method has been used for the alternating current motor control for the elevator system. As illustrated in FIG. 3, the conventional elevator system using the vector control method includes an alternating current power source AC and a converter 101 converting an alternating current from the alternating current power source AC into a direct current. A condenser 102 for smoothing a ripple component included in an output from the converter 101 is connected to the output from the converter 101. An inverter 103 for converting a direct current voltage outputted from the condenser 102 into an alternating current voltage is connected across the condenser 102. An alternating current motor 106 is connected to an output from the inverter 103 to be driven in a clockwise or counterclockwise by an alternating current supplied from the inverter 103. A sheave 108 is connected to an output axis of the alternating current motor 106, and rotated in a clockwise or counterclockwise. A rope winds around the sheave 108. A car 109 lifted/lowered in a hoist way for loading passengers or cargo is connected to one end of the rope, and a balance weight 110 balancing with the car 109 is connected to the other end of the rope. The following control units are additionally connected for the speed and leveling control of the conventional elevator system. Current detectors 104 are connected to a current supply path from the inverter 103 to the alternating current motor 106 in order to detect a current flowing through the motor 106. A pulse generator 107 detecting a rotation speed of the motor 106 and outputting a resultant pulse signal is connected to the output axis of the motor 106. A load detector 111 is disposed at a low portion of the load detector 111, and detects and outputs the load of the car 109.
As depicted in FIG. 2, a position detection unit 112 disposed at an upper portion of the car 109 includes a pair of position detectors PA, PB. Each position detector PA, PB is provided with a photo-coupler or a magnetic switch (not shown). On the other hand, a shielding plate SP is disposed at a predetermined height from each floor bottom surface of the walls of the hoist way, and detects a position of the car 109 by intercepting an optical transmission or magnetic flux of the position detectors PA, PB.
According to output signals from the position detectors PA, PB, a level difference detection unit 113 detects a state where the bottom level of the car 109 is identical to the bottom level of the designated floor (FIG. 2(a)), a state where the bottom level of the car 109 is higher than the bottom level of the designated floor (FIG. 2(b)) or a state where the bottom level of the car 109 is lower than the bottom level of the designated floor (FIG. 2(c)), thereby outputting an output signal corresponding to the respective states.
A level compensation operation command generator 114 is connected to an output from the level difference detection unit 113. When the level difference is generated as shown in FIG. 2(b) or 2(c), the level compensation operation command generator 114 outputs a corresponding lifting or lowering level compensation operation command signal LCD as shown in FIG. 3d according to an output signal from the level difference detection unit 113.
A speed command generator 115 is connected to an output from the level compensation operation command generator 114. In case the level compensation operation command generator 114 generates the lifting or lowering level compensation operation command signal LCD, the speed command generator 115 outputs a level compensation speed pattern signal LCV as shown in FIG. 3e.
A speed controller 116 is connected to an output from the speed command generator 115 and an output from the pulse generator 107, computes a speed difference of the motor 5 according to a speed command value of the level compensation speed pattern signal LCV from the speed command generator 115 and a pulse signal from the pulse generator 107, and outputs a torque component current command signal I.tau.* of the motor corresponding to the difference value.
A load current converter 117 is connected to an output from the load detector 111, and outputs a load compensation torque signal it_ub1 representing a detection load (a load resulting from a weight difference between the car 109 and the balance weight 110, which must be torque-compensated) from the load detector 111 as a current value.
A current controller 118 is connected to an output from the speed controller 116, an output from the current detector 104 and an output from the load current converter 117, and adds a current value corresponding to a detection load amount represented by the load compensation torque signal it_ub1 from the load current converter 117 into a difference value between a torque component current command value represented by the torque component current command signal i.tau.* from the speed controller 116 and a current value flowing through the motor 106 from the current detector 104, thereby outputting a current command signal it* corresponding to the torque amount to be finally compensated.
A pulse width modulator 119 is connected to an output from the current controller 118, generates a pulse width modulation signal corresponding to the current command signal it* from the current controller 118, provides the pulse width modulation signal to the inverter 103, and switching-controlling the inverter 103.
The leveling operation of the conventional leveling control device for the elevator system will now be explained with reference to FIGS. 1 to 4.
After the input alternating current power source AC is converted into a direct current voltage through the AC/DC converter 101, if the ripple component is removed by the condenser 102, it becomes an almost complete direct current voltage, and is applied to the inverter 103. The power semiconductor devices such as power transistors constituting the inverter 103 are switched to a predetermined pattern according to a switching control signal outputted from the switching signal generator 119, and thus convert the inputted direct current voltage into the alternating current voltage. The converted alternating current voltage is applied to the motor 106, thus driving the motor 106. The motor 106 rotates the sheave 108, and thus the car 109 and the balance weight 110 start a linear motion in the opposite direction. As a result, the car 109 starts to move toward the designated floor according to the switching signal supplied to the inverter 103.
In case the car 109 stops at the designated floor so that the bottom level of the car 109 can be identical to the bottom level of the designated floor, as shown in FIG. 2(a), the level compensation operation is not performed.
However, as shown in FIG. 2(b), when the bottom level of the car 109 is higher than the bottom level of the designated floor, the position detector PA of the position detection unit 112 is ON, but the position detector PB thereof is OFF. At this time, the door of the car 109 is opened. In addition, when the car 109 stops at the designated floor, if the bottom level of the car 109 is lower than the bottom level of the designated floor, the position detector PA is OFF, but the position detector PB is OFF.
As described above, in the case that the bottom level of the car 109 is higher or lower than the bottom level of the designated floor, according to the ON or OFF state signal of the position detectors PA, PB, the level difference detection unit 113 detects that the level difference is generated in an upward or downward direction, and outputs a signal showing this to the level compensation operation command generator 114. Thus, as shown in FIG. 3d, the level compensation operation command generator 114 outputs the level compensation operation command LCD in the upward or downward direction at the point ts.
Accordingly, the speed command generator 115 receiving the level compensation operation command LCD outputs the level compensation speed command LCV The LCV signal is increased in an exponential function method, as shown in FIG. 3e. The car 109 is operated at a constant speed Vs after the time ts. As shown in FIG. 2(a), when the bottom level of the car 109 is identical to the bottom level of the designated floor, the position detectors PA, PB are all OFF. Here, the level compensation operation command LCD is extinguished at the time tv as in FIG. 3, and the level compensation speed command LCV is reduced to zero (0) in the exponential function method.
On the other hand, the conventional leveling control operation for the elevator system will now be described with reference to FIG. 4. FIG. 4 is a block diagram illustrating main components of the conventional leveling control device for the elevator system as shown in FIG. 1. A subtracter 401 receives a speed command Wm* and an actual speed Wm, and outputs a difference. The speed controller 116 receives the difference, and outputs a torque command current i.tau.* in order to compensate the difference. While the level compensation operation is performed, the load current converter 117 outputs the load compensation torque current it_ub1 to an adder 402 in order to compensate the load detected by the load detector 111. The adder 402 adds the load compensation torque current it_ub1 and the torque current i.tau.*, and outputs the final torque command current it*. The final torque command current it* controls the motor 106 through a current controller and power rectifier 403. Here, the current controller and power rectifier 403 include the current controller 118, the pulse width modulator 119 and the inverter 103.
In an ideal case, the alternating current motor 106 can generate the torque command Tm corresponding to the final torque current it* (it*=i.tau.*+it_ub1) by the current controller and power rectifier 403. The torque command Tm must be identical to a weight difference between the car 109 and the balance weight, namely an unbalanced torque TL. However, the load detected by the load detector 111 has an error when the passengers get in or off at the designated floor. As a result, a mechanical system (movable mechanical system included in the elevator system, such as the car 109, balance weight 110, sheave 108 and rope) having an inertia due to a torque Tm-TL corresponding to the error of the load is accelerated. When it is presumed that the mechanical system is a rigid body, a mass thereof is J, a speed thereof is Wm, and an acceleration thereof is d Wm/dt=Wm.times.S (differential operator), the mechanical system is accelerated at an acceleration of Wm.times.S. The torque of the mechanical system moving at the acceleration is J.times.Wm.times.S. The speed Wm of the elevator car can be obtained by a multiplier of 1/(J.times.S). On the other hand, when the unbalanced torque TL is not identical to the load compensation torque current it_ub1 , that is when there is a difference between the load torque applied to the rotation axis of the motor 106 and the detection load detected by the load detector 111, the speed is varied as much as the difference, and the speed controller 116 outputs the torque current i.tau.* in order to reduce the speed variation. Here, in the case that a gain of the speed controller is sufficiently large, it is possible to rapidly respond to the speed variation. However, in the conventional elevator system, the gain of the speed controller 116 cannot be sufficiently increased due to a ride comfort. Accordingly, a big difference between the unbalanced torque TL and the load compensation torque current it-ub1 causes many problems in the level compensation operation. For example, as shown in FIG. 2(b), while the car exceeds the bottom level by a predetermined level in the upward direction from the reference position after the passenger gets off, and the level compensation operation downwardly is carried out, if the passenger gets in the car from the hall, the car 109 exceeds the bottom level by a predetermined level in the downward direction, and thus the level compensation operation is upwardly performed. Consequently, the level compensation operation time becomes longer.
Accordingly, in the speed control of the conventional elevator system, in case a load amount is sharply varied during the level compensation operation as the passengers get in or off, the speed is varied corresponding to the difference between the unbalanced torque TL and the load compensation torque, thereby more increasing the level difference. As a result, the level compensation operation time is increased, and furthermore the passengers may fall down. In addition, the difference between the unbalanced torque TL and the load compensation torque may be increased due to a response delay according to the structure of the load detector, a mis-detection of the load state, noise and a defect of the load detector.